1. Field of the Invention
This invention relates to a clamp, and more particularly, it relates to a clamp having an adjustable workpiece engaging presser member whereby the clamp may be used on workpieces of varying thicknesses.
2. Description of Related Art
In the sewing industry, it is common to provide a clamp at a sewing station to firmly hold a workpiece in position on a support surface underneath a sewing head whereby workpieces may undergo a repetitive sewing operation with the clamp operating to engage with each of the workpieces prior to the sewing operation being initiated. Typically, the supporting surface and lower surface of the clamp for engaging the workpiece are substantially planar such that a workpiece have a uniform thickness will be clamped with a substantially uniform clamping force by the clamp.
An example of a typical prior art clamp is seen in U.S. Pat. No. 4,763,587 which shows a clamp frame movable in a vertical direction for engagement with and disengagement from a workpiece. The frame forms a boundary around a central sewing area to facilitate the prevention of tenting during the sewing operation.
A problem associated with prior art clamps is that a workpiece having a varying thickness through the clamped area will not receive a uniform clamping force. Thus, it is possible for a workpiece of variable thickness to be improperly clamped such that the sewing of the workpiece may be adversely affected if the workpiece should move relative to the clamp.
Still another problem of prior art clamps is that the clamping pressure applied by the clamp is not adjustable at the clamping surface such that a smaller clamping force may be applied to a thin workpiece than to a thick workpiece.